The invention relates to a method and apparatus for performing the settingup of a fault-signal evaluating circuitry in an apparatus which detects the presence of unacceptable faults in and/or on a hollow body of transparent material.
The transparent material in question would in particular be glass or plastic. The faults to be detected would include cracks, contaminants, bubbles, holes, improperly formed mouths, as well as deviations from proper dimensions and configuration, such as tilted mouths, improper ovalness, anticlinal formations and improper length.
For example, cracks can be present in hollow glass articles in an almost unlimited variety of spatial orientations. However, in actual practice, cracks will tend to appear most often in certain zones of the article, determined by the production process involved. For each different type of hollow glass article, different typical crack orientations will predominate. There has been no reliable, simple and automatable procedure for locating all cracks in the series of hollow glass articles produced in a production run irrespective of type of article and types of cracks and of general applicability, such as for example impact and acoustical detection methods.
U.S. Pat. No. 3,687,559 discloses an optical method of detecting faults in hollow glass articles. A plurality of light beams are deflected onto respective zones of a hollow glass article to be tested. Photoelectric transducers are positioned in association with these zones, and if located in the dark receive light signals produced by a fault. An idealized crack forms, for example, a reflecting plane. A light source of fixed spatial orientation determines relative to this plane the location for the photoelectric transducer. If the orientation of the crack is different, the light source and/or transducer must be differently positioned. This applies to each zone of the hollow glass article to be examined. Because faults are most often located within the body of glass itself, there occurs in addition to reflection effects a refraction of the test light beam at the air-glass and glass-air interfaces, unless the test beam is incident normal to the surface of the hollow glass article. This refraction effect still further complicates the problem of properly performing the setting-up of the apparatus. Because of the innumerable possibilities as to the shapes of the faults and their orientations, one must limit oneself in actual practice to certain critical zones on the hollow glass body. Nevertheless, because of increasingly demanding industrial standards with respect to fault detection, an ever-growing number of light sources and photoelectric transducers is being required.
According to one prior-art setting-up technique, each of this plurality of testing channels in a single testing apparatus must be adjusted by a set-up technician possessed of exceptional aptitude for the visualization of geometrical and optical relationships and having furthermore considerable electronics expertise, who properly adjusts the positions and orientations of testing-channel components, selects proper sensitivity levels, and so forth. The task of such a set-up technician is greatly complicated by the fact that faults located in a zone associated with one testing channel of the apparatus may have an effect upon the detection of faults in zones associated with others in the testing channels. In addition, the industry seeks more and more to be able to detect smaller and smaller faults, creating increasingly difficult demands as to sensitivity and precision of detection.